1. Field of the Invention
This invention relates to a method of producing a storage stable, one part, heat curable organosilicon composition through the in situ production of a cure inhibitor.
2. Description of the Prior Art
In U.S. Pat. No. 3,989,667, issued Nov. 2, 1976, by Lee et al., a polyorganosiloxane is described which is a platinum catalyst inhibitor at room temperature but not at elevated temperature. Also described is a curable organosilicon composition having the polyorganosiloxane as one of the ingredients.
Several methods for making the polyorganosiloxane of Lee et al. are described in the patent. The best method is stated to be that taught in U.S. Pat. No. 3,933,880, issued Jan. 20, 1976, by Bergstrom, Lee, and Maxson. The polyorganosiloxane is prepared by continuously passing a mixture of an acetylenic alcohol, a platinum catalyst, and a siloxane compound having at least three silicon-bonded-hydrogen atoms through a heating means wherein the mixture is heated above 100.degree. C. and above the temperature at which the reaction product no longer inhibits the reaction, which is under sufficient pressure to maintain the reaction mixture in the liquid state, and recovering the polyorganosiloxane.
The method of the Bergstrom et al. patent requires specialized equipment capable of operation at elevated temperatures and pressures. The method also requires distillation under reduced pressure to remove unreacted material.
U.S. Pat. No. 3,989,666, issued Nov. 2, 1976, to Niemi discloses a method of preparing a crosslinker-platinum catalyst-inhibitor composition comprising mixing a siloxane having an average of at least three silicon-bonded hydrogen atoms per molecule, an acetylenic alcohol, and a platinum catalyst to form a mixture, heating the mixture in a closed system for 10 to 30 hours at a temperature of from 50.degree. C. to 90.degree. C., and thereafter removing unreacted acetylenic alcohol by applying a reduced pressure of 700 to 750 mm of mercury for at least 10 hours at a temperature of from 20.degree. C. to 30.degree. C. The patent further discloses a curable composition comprising an organosilicon polymer having an average per molecule of at least two monovalent hydrocarbon radicals containing aliphatic unsaturation, and the crosslinker-platinum catalyst-inhibitor composition prepared by the above method.
The method of Niemi manufactures a crosslinker-platinum catalyst-inhibitor composition which is subsequently used as an ingredient in a curable composition. The composition of the curable composition is restricted in that the ratio of platinum catalyst, acetylenic alcohol, and siloxane having at least three silicon-bonded hydrogen atoms per molecule is predetermined at the time of manufacture of the crosslinker-platinum catalyst-inhibitor composition. No method of adjusting the ratio of aliphatic unsaturation on the organosilicon polymer to reactive groups in the crosslinker-platinum catalyst-inhibitor composition is provided for that does not also upset the property of inhibition and causes one to lose the advantages gained from the Niemi composition.